fix: expose rejected incoming payment requests

[ovitrif]

Parent: #1207
Source: Pubky marketplace Bitkit team brief
Counterpart: synonymdev/bitkit-ios#714

Scope

• Add redacted, reason-specific diagnostics for parse-time rejection.
• Implement the shared requested/open-time failure UX after retries exhaust.

Acceptance criteria

• Behavior and localized user outcomes match the iOS contract.
• Unit tests cover parse and resolution failures.